Heating, ventilation and air conditioning systems are commonly used in both residential and commercial environments to control indoor air temperature. In geographical areas experiencing cold or humid conditions, the circulation of heated air through air ducts and into a home or office provides comfort and improves occupants' health.
In order to heat air to be circulated into an indoor environment, many heating systems utilize gas-fired hot air furnaces. Gas-fired furnaces typically include a heat exchanger made up of a plurality of heat exchanger tubes. Each of the tubes defines an internal flow path through which hot combustion gases are circulated. The walls of the heat exchanger tubes are thereby warmed through conduction. Air is then forced externally over the outer walls of the heat exchanger tubes whereupon the air is warmed and circulated into the indoor environment.
In order to produce the hot combustion gases, a fuel-gas is fed through a manifold in the furnace. The manifold has a plurality of outlets corresponding with the number of heat exchanger tubes employed. Interposed between the heat exchanger tubes and the manifold outlets are a plurality of burners. The burners are provided in one-to-one correspondence to the number of heat exchanger tubes. The burners may be of conventional construction such as the type shown in U.S. Pat. No. 6,196,835.
In operation, the air/fuel-gas mixture is pulled across the burners and into the associated heat exchanger tubes at an inlet end. Each burner typically includes an opening defining a venturi device that provides for the proper mixture of air and fuel-gas. The air and fuel-gas are received and combined at one end of the burner adjacent the manifold, and the air/fuel-gas mixture is ignited at the opposite end of the burner at a burner port.
As a part of the injection process, additional air is drawn into the heat exchanger so that the fuel-gas may be fully combusted within the heat exchanger. An induction draft fan is placed at an opposing outlet end of the heat exchanger in order to create negative pressure relative to the burner ports. The induction draft fan may be a single fan that is manifolded to the various heat exchanger tubes by a header so that negative pressure is applied to each heat exchanger tube by a single fan. The application of negative pressure by the fan causes the ignited air/fuel-gas mixture to flow into and through the respective heat exchanger tubes. The fan also produces a positive exhaust pressure to discharge the heated gases from the heat exchanger to a discharge flue.
The tubular heat exchangers are commonly arranged in a serpentine pattern to increase surface area. At the same time, the tubular bodies are spaced-apart to allow external air to flow therebetween. In operation, a blower is provided as part of the heating system. The fan pulls (or pushes) cold room air from the area that is to be heated, and forces that air across the outer surfaces of the heat exchanger surfaces. The air is then pumped through air ducts and into the rooms to be heated.
Referring to FIGS. 1 and 2, typically mechanically exhausted heat exchangers of the clam shell or tubular variety have a heat exchanger inlet end attached to a header. With clam shell heat exchangers such as shown in FIG. 1, the header forms a swaged collar with the end of the heat exchanger (FIG. 1). In the tubular variety, the heat exchanger end is crimped or formed to tightly engage through an opening in the header (FIG. 2). These various steps of swaging and forming cause an irregular surface at the entrance to the heat exchanger inlet. As shown in FIGS. 1 and 2, the irregular surface causes turbulence specifically with regard to entry of secondary combustion air into the primary air/gas mixture. The secondary combustion air is shown by solid arrows and the flame is shown by dotted arrows in FIGS. 1 and 2. Thus, partial products of combustion are created in the early stages of the combustion process due to this turbulent secondary air. Furthermore, the turbulence has a deleterious effect on the combustion process resulting in creation of carbon monoxide and nitrous oxide compounds. Both carbon monoxide and nitrous oxide compounds are undesirable by-products of the combustion process and various industry standards exist which limit the levels of these products. It is contemplated that a less turbulent flow of secondary combustion air when mixing with the primary air gas mixture as the flame enters the heat exchanger will reduce the quantity of carbon monoxide and nitrous oxide compounds produced.
There is therefore a need for an apparatus which will result in a less turbulent flow of secondary combustion air when mixing with the primary air gas mixture upon entry into the heat exchanger.
During periods of cold weather, the hot air furnace operates with some degree of frequency to warm the indoor environment. This has the effect of keeping heated combustion gases moving through and drying the interior combustion chamber walls of the heat exchanger. However, during periods of warmer weather, particularly during the summer months, the furnace may not operate for an extended period of time. This permits warm, high-humidity air to enter the inlets of the heat exchanger tubes. Those of ordinary skill in the art will understand that the interior portion of the heat exchanger of separated combustion units will oftentimes contain outdoor air independent of whether the heater is installed indoors or outdoors. During periods of warm weather when the HVAC system operates in a cooling mode, cooled air is drawn across the combustion chamber walls. This cooled air is usually at a temperature that is below the outdoor air temperature and more importantly below the temperature of air that is inside of the heat exchanger. The result is that high-humidity outdoor air that is inside the heat exchanger condenses and forms droplets of moisture, or “condensates,” on the interior walls. The condensates flow down the walls of the tubular heat exchangers and may drip in and around the burner ports of the hot air furnace. The burner ports are primarily fabricated from alloys of metal, and are subject to corrosion when exposed to condensates for extended periods of time. In many instances, burner ports must be replaced prematurely before cooler weather returns to the area and the HVAC system is placed in a heating mode.
There is, therefore, a need for an apparatus that will prevent condensates from collecting around burner ports. There is further a need for a plate that may be positioned above burner ports to intercept condensation before it hits the burner ports and divert the condensation out of the furnace.